individually. Although, this is a good approach to quantifying the predation potential
of a single stage of a species, all life stages should be employed to reach a right
conclusion. It has rarely been seen in nature that only one predatory stage kills
the prey.
The other artifact of this kind of experiment is that it does not permit detection of
mutual interference on number of prey killed. Actually, only in one case, two
predator individuals have been used in F.R. experimental unit. The results showed
it decreased searching efficiency but not handling time relative to the classic
F.R. experiments used only one predator individual. Moreover, in most cases, a
complex of aphidophagous predators present in a prey patch and compete with each
other for shared prey. Under experimental condition, the effects of intra- and
interspecific competition could not be clarified. Solving this problem could be
done with prey labeling, i.e., if possible, prey labeled with traceable colors, proteins,
or radioactive compounds in a way that number of killed prey by each stage could be
estimated. This design also improves the reality of experiments because the effect of
mutual interference among different predatory stages could be evaluated. Finally,
the spatial distribution of predator and prey is a crusial factor affecting the predation
rate that could not be simulated in Petri dish based experiments. Table 2.3 shows
there are some variations in searching efficiency and handling time with regard to
prey species and experimental arena. As would be expected, the immature stages of
H. variegata influenced more intensively by small experimental arena than adults.
This might be because adult body size is too large to be influenced by leaf area extent
or host plant physical traits. Only in one case (Jafari and Goldasteh 2009) the
searching rate was very small compared to other studies. This difference might be
attributed to size of experimental unit. In their studies the volume of threedimensional experimental arena searched by females was 1518 cm
3 while in most
two dimensional experiments (leaf discs) the searching area volume was not more
than about 80 cm
3 approximately.
Another F.R. parameter (the handling time) shows high variations among different studies. It ranges from low and biologically unrealistic values as 1 Â 10
À8 h to
high value as 1.9 h. This variation seems inconceivable; because it means that one
third instar larva spents about 114 min in non-searching activities (pursuing, feeding,
digesting, grooming and resting) for a single prey. Conversely, in another study,
fourth instar larvae spent nearly zero time for handling the prey that clearly it is
unrealistic and resulting from artificial data gathering and analyzing. The handling
time of H. variegata female showed less variations and it was more congruent.
The one point that tended to be overlooked in some F.R. experiments is that some
lack any control to correct treatment mortality. Of course, control mortality is
negligible but considering control mortality would be increased results accuracy.
Other issue that should not be ignored in comparing the results of functional
response studies is that those studies conducted at different parts of Iran and lady
beetles used have been collected from different elevations and climates. It has been
shown that variegated lady beetle or spotted amber ladybird shows variations in their
wing size regarding their origins (Abdollahi Mesbah et al. 2015); therefore it is
possible that local populations composed of different morphs with diverse biological
2 Lady Beetles; Lots of Efforts but few Successes
63
of a single stage of a species, all life stages should be employed to reach a right
conclusion. It has rarely been seen in nature that only one predatory stage kills
the prey.
The other artifact of this kind of experiment is that it does not permit detection of
mutual interference on number of prey killed. Actually, only in one case, two
predator individuals have been used in F.R. experimental unit. The results showed
it decreased searching efficiency but not handling time relative to the classic
F.R. experiments used only one predator individual. Moreover, in most cases, a
complex of aphidophagous predators present in a prey patch and compete with each
other for shared prey. Under experimental condition, the effects of intra- and
interspecific competition could not be clarified. Solving this problem could be
done with prey labeling, i.e., if possible, prey labeled with traceable colors, proteins,
or radioactive compounds in a way that number of killed prey by each stage could be
estimated. This design also improves the reality of experiments because the effect of
mutual interference among different predatory stages could be evaluated. Finally,
the spatial distribution of predator and prey is a crusial factor affecting the predation
rate that could not be simulated in Petri dish based experiments. Table 2.3 shows
there are some variations in searching efficiency and handling time with regard to
prey species and experimental arena. As would be expected, the immature stages of
H. variegata influenced more intensively by small experimental arena than adults.
This might be because adult body size is too large to be influenced by leaf area extent
or host plant physical traits. Only in one case (Jafari and Goldasteh 2009) the
searching rate was very small compared to other studies. This difference might be
attributed to size of experimental unit. In their studies the volume of threedimensional experimental arena searched by females was 1518 cm
3 while in most
two dimensional experiments (leaf discs) the searching area volume was not more
than about 80 cm
3 approximately.
Another F.R. parameter (the handling time) shows high variations among different studies. It ranges from low and biologically unrealistic values as 1 Â 10
À8 h to
high value as 1.9 h. This variation seems inconceivable; because it means that one
third instar larva spents about 114 min in non-searching activities (pursuing, feeding,
digesting, grooming and resting) for a single prey. Conversely, in another study,
fourth instar larvae spent nearly zero time for handling the prey that clearly it is
unrealistic and resulting from artificial data gathering and analyzing. The handling
time of H. variegata female showed less variations and it was more congruent.
The one point that tended to be overlooked in some F.R. experiments is that some
lack any control to correct treatment mortality. Of course, control mortality is
negligible but considering control mortality would be increased results accuracy.
Other issue that should not be ignored in comparing the results of functional
response studies is that those studies conducted at different parts of Iran and lady
beetles used have been collected from different elevations and climates. It has been
shown that variegated lady beetle or spotted amber ladybird shows variations in their
wing size regarding their origins (Abdollahi Mesbah et al. 2015); therefore it is
possible that local populations composed of different morphs with diverse biological
2 Lady Beetles; Lots of Efforts but few Successes
63